Conventionally, in transport lines for liquids in the semiconductor industry, bio and medical industries, food industry, and other chemical industries, use has been made of ball valves comprised of balls provided in the valve chests and gripped by seat carriers fitted with seat rings, and pocket-less ball valves comprised of balls arranged rotatably in a casing formed with a spherical space inside so as not to form pockets therein.
In these conventional ball valves, when the valves were left open to pass the fluid therethrough for long periods, the connection between the space formed between the valve chest and the ball and the passage of the liquid is completely shut, whereby the liquid sealed in the space becomes completely dead (stagnant), and thus it becomes impossible to prevent a proliferation of bacteria, etc.
Further, a pocket-less ball valve has a large rotational torque, since substantially the entire ball surface serves as a sliding part, but to ensure a smooth operation thereof, the machining precision of the ball and the spherical space must be very strict. Further, from a micropoint of view, since sliding parts are used, when water enters therein it becomes impossible to prevent a proliferation of bacteria, etc.
Further, in the conventional ball valve, when the valve is closed, fluid flowing into the valve chest space stagnates, as it is closed off from the ambient atmosphere, and this sometimes causes problems. For example, in the semiconductor industry, hydrogen peroxide water is sometimes flushed through pipes to sterilize the insides of the pipes, but if the ball valve is closed after passing the fluid therethrough, the hydrogen peroxide water sealed in the valve chest is vaporized and the pressure in the valve chest rises, causing problems of cracks in the ball valve body and a breakage of the seat rings.